1. Field of the Invention
The present invention relates to a technique for packet protection in a packet transfer ring.
2. Description of the Related Art
With an increase in data system traffic whose representative is IP, efficient transmission of data is demanded from conventional communication service providers (hereinafter referred to as carriers) which provide transmission service mainly for voice. Together with the demand, as highly reliable protection method as “SONET, GR-1230-Core, Issue 3 Dec. 1996 Bellcore” on which conventional transmission networks base is demanded also in a data transmission network. Among highly reliable protection methods in data transmission networks is Spatial Reuse Protocol (hereinafter referred to as SRP)(RFC 2982 IETF).
With reference to FIGS. 22 to 25, a protection method using the conventional SRP will be described.
FIG. 22 is a block diagram showing an example of a structure of a transmission device which executes protection using the SRP. A transmission device 100 includes link monitors 110 and 111, a failure information collection unit 120, Add/Drop 130 and 131, Wrap switches 140 and 141, frame conversion units 150 and 151, inverse frame conversion units 152 and 153, Trb-UNI switches (UNI tributary packet switches) 160 and 161 and a UNI forwarding table 170.
The link monitors 110 and 111 each monitor a failure condition of an input link 101-IN of an inner ring and an input link 102-IN of an outer ring and when detecting a failure, notify the failure information collection unit 120 of link failure information indicative of the detected failure.
When notified link failure information by the link monitors 110 and 111, the failure information collection unit 120 generates a ring network failure information notification packet containing the link failure information and transmits the packet to other transmission device through the Add/Drop 130 and 131, as well as switching an operation mode of the Wrap switch 140 or the Wrap switch 141 from a pass mode to a Wrap mode according to the input link having the failure. When the failure occurs in the input link 101-IN, switch the Wrap switch 141 to the Wrap mode and when the failure occurs in the input link 102-IN, switch the Wrap switch 140 to the Wrap mode.
When a ring network failure information notification packet sent from other transmission device indicates that a failure occurs in an output link of the inner ring or the outer ring directly connected to its own transmission device 100, the failure information collection unit 120 switches the operation mode of the Wrap switch 140 or the Wrap switch 141 from the pass mode to the Wrap mode according to the output link in which the failure occurs. When the failure occurs in an output link 101-OUT of the inner ring, switch the Wrap switch 140 to the Wrap mode and when the failure occurs in an output link 102-OUT of the outer ring, switch the Wrap switch 141 to the Wrap mode.
The Add/Drop 130 and 131 decipher a kind of an NNI packet (packet for use in a ring) applied from the link monitors 110 and 111, the Wrap switches 140 and 141, the Trb-UNI switches 160 and 161 or the failure information collection unit 120 and a transfer destination NNI address of the NNI packet and when the kind indicates a ring network failure information notification packet, drop the packet into the failure information collection unit 120, when the kind indicates a data packet which is an NNI packet to be terminated at its own transmission device, drop the packet into the inverse frame conversion units 152 and 153 and when the kind indicates other kind of NNI packet, pass the packet through the Wrap switches 140 and 141. Here, to the transmission device 100, two MAC addresses #A and #B are assigned and the Add/Drop 130 drops only an NNI packet whose transfer destination NNI address is #A into the inverse frame conversion unit 152, while the Add/Drop 131 drops only an NNI packet whose transfer destination NNI address is #B into the inverse frame conversion unit 153.
The Wrap switches 140 and 141 have their modes controlled by the failure information collection unit 120 and transfer NNI packets applied from the Add/Drop 130 and 131 to the output links 101-OUT and 102-OUT of the inner ring and the outer ring, respectively, at the time of the pass mode and transfer the same to the Add/Drop 131 and 130, respectively, at the time of the Wrap mode.
When a UNI packet (user packet sent from a network or a terminal connected to a tributary port) is sent through the Trb-UNI switch 160, the frame conversion units 150 and 151 derive a transmission destination NNI address based on its transmission destination UNI address, convert the packet into an NNI packet having the transmission destination NNI address and a predetermined transmission source NNI address and transfer the obtained packet to the Add/Drop 130 and 131. The frame conversion unit 150 applies #A as a transmission source NNI address of the NNI packet and the frame conversion unit 151 applies #B as a transmission source NNI address of the NNI packet.
The inverse frame conversion units 152 and 153 convert an NNI packet into a UNI packet and send the converted packet to a tributary port 103-OUT.
The Trb-UNI switches 160 and 161 transfer a UNI packet to a desired output port with reference to a transfer destination address of the UNI packet and the UNI forwarding table 170.
FIGS. 23A and 23B show two-fiber rings with transmission devices 100-1 to 100-6 connected in a ring through an inner ring 101 and an outer ring 102. Each of the transmission device 100-1 to 100-6 has the same structure as that of the transmission device 100 shown in FIG. 22. In addition, the inner ring 101 is composed of links 101-1 to 101-6 to transfer a packet counterclockwise and the outer ring 102 is composed of links 102-1 to 102-6 to transfer a packet clockwise.
With reference to FIGS. 23A and 23B, description will be made of an SRP protection method in a case where a failure occurs in the links 101-5 and 102-5 between the transmission devices 100-5 and 100-6. It is assumed that before the failure occurs, a UNI packet sent from a terminal 210 is converted into an NNI packet at the transmission device 100-1 and after being transferred to the transmission device 100-4 through the inner ring 101, again converted into a UNI packet and then transferred to the terminal 211 as indicated on a path 201 shown in FIG. 23A.
When detecting failures in the links 101-5 and 102-5, respectively, the link monitors 110 and 111 of the transmission devices 100-5 and 100-6 notify the failure information collection units 120 in their own devices of the failures.
Responsively, the failure information collection unit 120 of the transmission device 100-5 switches the Wrap switch 141 from the pass mode to the Wrap mode. The failure information collection unit 120 also generates a ring network failure information notification packet indicative of a failure occurring in the link 101-5 and sends the packet to the inner ring 101 through the Add/Drop 130.
In the same manner, the failure information collection unit 120 of the transmission device 100-6 switches the Wrap switch 140 from the pass mode to the Wrap mode. The failure information collection unit 120 also generates a ring network failure information notification packet indicative of a failure occurring in the link 102-5 and sends the packet to the outer ring 102 through the Add/Drop 131.
The failure information collection units 120 of other transmission devices than 100-5 and 100-6 refer to the ring network failure information notification packets notified through the inner ring 101 and the outer ring 102 to transfer the packets as they are to the subsequent transmission devices.
Upon receiving the ring failure information notification packet indicating that a failure occurs in the link 102-5 which is sent from the transmission device 100-6, the failure information collection unit 120 in the transmission device 100-5 switches the Wrap switch 141 to the Wrap mode when the switch is at the pass mode. Since the switch is already at the Wrap mode in this case, no mode switching processing is conducted. Squelching of the ring network failure information notification packet is also conducted.
Similarly, upon receiving the ring failure information notification packet indicating that a failure occurs in the link 101-5 which is sent from the transmission device 100-5, the failure information collection unit 120 in the transmission device 100-6 switches the Wrap switch 140 to the Wrap mode when the switch is at the pass mode. Since the switch is already at the Wrap mode in this case, no mode switching processing is conducted. Squelching of the ring network failure information notification packet is also conducted.
As a result, the NNI packet sent from the transmission device 100-1 is transferred from the transmission device 100-1 to the transmission device 100-6 by using the inner ring 101, then turned back at the transmission device 100-6 as indicated in the path 202 shown in FIG. 23B, passed in the outer ring 102 through the transmission devices 100-1 to 100-4, again wrapped by the transmission device 100-5 and transferred to the transmission device 100-4 by using the inner ring 101. The NNI packet applied through the inner ring 101 to the transmission device 100-4 is converted into a UNI packet and then transferred to the desired terminal 211.
By thus using the SRP protection method, even when a fiber failure occurs, packets can be transferred to a desired transmission device by detouring around a failure section.
Since in SRP protection, a packet is wrapped by transmission devices at opposite ends sandwiching a failure point, at a section between one wrap point and a transmission source transmission device (i.e. a section between the transmission device 100-6 and the transmission device 100-1 in FIG. 23B) and a section between the other wrap point and a reception side transmission device (i.e. a section between the transmission device 100-4 and the transmission device 100-5 in FIG. 23B), twice a band is required for transferring a certain NNI packet to result in deteriorating band efficiency.
In the SRP protection method, when the transmission device 100-4 has a transmission failure as shown in FIG. 24A or when a multiple failure occurs at the links 101-3, 101-4, 102-3 and 102-4 as shown in FIG. 24B, an NNI packet transferred from the transmission device 100-1 to the transmission device 100-4 is wrapped at the transmission devices 100-3 and 100-5 at the opposite ends sandwiching the failure occurring position, so that it can not reach the transmission device 100-4 and makes a round of the network to be terminated at the input link 101-1 of the transmission source transmission device 100-1. When the NNI packet is thus unable to reach the transfer destination transmission device (when the NNI packet becomes an unreachable packet), the NNI packet wastefully uses a network band.
Also when the network is arranged such that a terminal 211 is connected to an Ethernet switch 410, and the Ethernet switch 410 and the transmission devices 100-4 and 100-3 are connected (dual homing) through an actual use port 401 and a spare port 402, respectively, as illustrated in FIG. 25, since a transmission destination address of an NNI packet to be transmitted to the terminal 211 is a MAC address applied to the transmission device 100-4, the transmission device 100-3 is unable to recognize the NNI packet as a self-addressed NNI packet and is therefore unable to process the NNI packet. As a result, when the transmission device 100-4 connected to the actual use port 401 has a transmission device failure, although a transfer path exists from the terminal 210 to the terminal 211 using the spare port 402, the packet becomes an unreachable NNI packet to result in deteriorating a failure recovery rate.